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achromatic angles of incidence aperture astigmatism astronomical telescope axes axis becomes bright point caustic centre characteristic function circle concave concave lens conjugate foci convex lens cornea cos2 crystalline lens curvature curve cylinder denote determined dispersion distance distinct vision emergent pencil emergent ray equal equation eye-glass eye-lens eye-piece field of view focal length focal lines glass horopter incidence and refraction incident pencil incident ray instrument lenses luminous point magnifying power measured medium minimum deviation nodal points normal object object-glass optical parhelic circle perpendicular placed position principal focus principal plane principal points principal ray prism quantities radii radius ray of light ray passes reflected rays reflexion refracting angle refracting surface refractive index respectively retina seen sin2 small pencil spectrum sphere spherical aberration spherical surface standard ray suppose tangent thin lens vertical
Page 3 - Let f(ff) oe the intensity of emission per unit area in a direction making an angle 0 with the normal to the element ; then the whole amount of light transmitted to the eye when the element is inclined to the line of sight at an angle 0 is <B sec 0 .f(0).
Page 233 - The space between the cornea and the crystalline lens is filled with a transparent fluid resembling water, and thence termed the aqueous humour. The space between the crystalline lens and the retina is filled with another transparent fluid, somewhat more viscous than the former, and called the vitreous humour. These two humours, like the crystalline lens, are contained in transparent membranous capsules of great delicacy. In their refractive indices the aqueous and vitreous humours differ very little...
Page 16 - ... the refracted ray ; and the acute angles which they make with the normal to the surface of separation at the point of incidence, are called the angles of incidence and refraction, respectively. The angles of incidence and refraction lie always in the same plane, and their sines are to one another in an invariable ratio. This is the fundamental law of refraction.
Page 265 - ... angle which it subtends. In the case of telescopes, the comparison is between an object as seen in the telescope, and the same object as seen with the naked eye at its actual distance. In the case of microscopes, the comparison is between the object as seen in the instrument, and the same object as seen by the naked eye at the least distance of distinct vision, which is usually assumed as 10 inches. But two discs, whose diameters subtend the same angle at the eye, may be said to have the same...
Page 266 - Wollaston was the first to use a combination of two lenses instead of a single lens; this combination is still known as Wollaston s Doublet. It was suggested by an inverted Huyghens. eye-piece, to be described presently. It consists of two planoconvex lenses whose focal lengths are in the proportion of 1 : 3, the plane surfaces being turned towards the object, and the lens of shorter focal length being placed next the object. The distance between the lenses can be adjusted to suit different eyes,...
Page 33 - If n equal and uniform prisms be placed on their ends with their edges outwards, symmetrically about a point on the table, find the angle of each prism in order that a ray refracted through each of them in a principal plane may describe a regular polygon. Show that the distance of the point of incidence of such a ray on each prism from the edge of the prism, bears to the distance of each edge from the common centre the ratio of 1 n T 2 - 2u cos - 9.
Page 233 - From what has been previously said, it follows that this total refractive index is greater than that of the nucleus. The increase of refracting power from the outer portions to the inner portions of the lens serves partly to correct the aberration, by increasing the convergence of the central rays more than that of the extreme rays of the pencil.
Page 268 - In a word, the greater the distance of the object the smaller the image. The angle AOB is called the visual angle; in general, it is the angle which the object subtends at the centre of the crystalline lens.
Page 198 - ... illumination at any point. 13. A straight line passes through the point of intersection of three rectangular reflecting planes, and is equally inclined to each of them; find the series of images produced, and distinguish between those resulting from one, two, and three reflexions respectively. 14. The image of a straight line perpendicular to the axis of a convex lens at a very great distance from it, approximates to a parabolic curve, whose equation is 2 (*+/)the centre of the lens being the...